Level 42-43 wilderness, you need to use telekinetic grab to get them. Can be bought from high-level Magic shops and made using the Runecrafting skill.
Thieved from chests located in Ardougne and Rellekka. You need level 28 Thieving and it earns 25 XP. You can telegrab this from small islands in Rellekka (the rock crab beach north of the sand pit); every time you telegrab you get 2. Also a monster drop.